Constant width synchronized pulse generator



E. LABIN ETAL Sept. 24, 194

CONSTANT W IDTH SYNCHRONIZED PULSE GENERATOR I 2 Sheets-Sheet 2 FiledFeb. 5, 1942 1 mV 6 Y m m m E E DIPPPPD m m 9 (444144 W M a n I]! as I Mw A I- E p km mm 7 1;?

m u [W Moi/r 6. m1 g E T v m A W 4 Wm M PI? Patented Sept. 24, 1946CONSTANT WIDTH SYNCHRONIZED PULSE GENERATOR Emile Labin and Donald D.Grieg, New York, N. Y,, assignors to Federal Telephone and RadioCorporation, a corporation of Delaware Application February 3, 1942,Serial No. 429,376v

2 Claims.

- 1 This invention relates to impulse generating systems and inparticular to an improved type of synchronized impulse generator fortiming, calibrating, and other control purposes. The invention isconsidered particularly adaptable where a highly accurate timinginterval is desired, as for example in aircraft identifier apparatuswherein small time intervals indicative of distance are observed on thescreen of a cathode ray tube. Such apparatus has been disclosed, forexample, in the copending applications Ser. Nos. 382,391 filed March 8,1941, and Ser. No. 383,108, filed March 13, 1941, of E. Labin.

It is an object of the invention to provide a method and n'fe'ans forgenerating accurately synchronized impulses over a relatively wide rangeof desired impulse recurrent frequencies. Another object is to providean improved form of constant-width impulse generator wherein forgenerating impulses of a desired controllable duration. 7

Other objects and various further features of novelty and invention willhereinafter be pointed out or will become apparent from a reading of thefollowing specification in connection withthe drawings includedherewith. In said drawings, Fig. 1 is a block diagram illustrating veryschematicallya preferred'form of the invention,

Figs. la, b 1 indicate wave form treat merit through the variouselements of the circuit of Fig. 1;

Fig. 2 represents schematically and in more detail certain of. theelements of Fig. 1;

Fig. 3 represents schematically and in more detail further elements ofFig. 1; and

Figs. 4a, b, e illustrategraphically certain circuitconditions occurringduring a normal operation of the apparatus of Fig. 3.

Broadly speaking, the invention contemplates the use of a masteroscillator of relatively high stability and having a generallysinusoidal wave form as theprime source of control energy. The

periodicity of this Wave form is related by a'simple factor to thedesired pulse width or duration in the output of the apparatus. Thissinusoidal wave form may be employed in a known manner to generate aseries of extremely equal or factoriall-y" related to the desired pulsewidth. The synchronizing impulses thus obtained are then supplied to anovel multi-vibrator circuit forming part of this invention, to generateimpulses of the desired shape and duration, that is, impulses equal. orfac-torially related in duration to the periodicity of thesynchronizing, this relationship being dependent upon circuitadjustments. Thereafter, the output may be suitably shaped for whateverthe required purposes.

For a more specific consideration, reference will now be made to Fig. 1,which shows in block diagram form, features of a preferred embodiment.As the master oscillator, we employ in the form shown, a quartzoscillator III to produce the required sinusoidal wave form. This. waveis then suitably shaped in .an inverter unit II for application to afull-wave rectifier I2 to give a balanced rectified output. Since themost accurately defined recurrent portion of the ouput of rectifier I2is the cusp-shaped part where the wave hits zero voltage, we accentuatethese cusps by applying the output of rectifier I2 to a pair ofsuccessive differentiator circuits I3 and I4, whereby in accordance withknown principles, a series of extremely sharp alternately positive andnegative impulses is produced. Since it is desired to use only one ofthese sets of impulses for synchronizatiom'output of diiferentiator I4is applied to a clipper or limiting device I5 to produce a series ofuni-directional synchronizing impulses.

These synchronizing impulses, as above-indicated,'may then be applied toa multi-vibrator circuit I6, which forms an important part of thisinvention. Since it is preferable that the impulses'applied tot-he inputof multi-vibrator it are positive and of a controllable magnitude,suitable networks I! and I8, including a phase reverser and cathodefollower, respectively, may be included in the circuit between clipperI5 and multi-vibratcr l6. Afterthe desired kind of impulse energy hasbeen formed in multi-vibrator I6, the output may be appropriatelyshaped, phased, and amplified for the required purposes in networks I9,26, and 2!, respectively.

Turning now to a more detailed consideration of the various elementsinvolved in the circuit of Fig. 1, reference is made to Fig. ,2 in whichoscillator i0 is seen to include a quartz crystal 22 and a pent'ode Tihaving certain resistance R2 in its output circuit Illa. Since thestability of the entire system is seen to depend .to a large 'extent onthe inherent stability of the master oscillator stage IB, it isconsidered preferable that certain precautions be taken to ensure thenecessary stability. For this reason, the resistance R2 may be includedin the output of tube T1 so that, should there be any impedance changeswithin tube T1 under operating conditions, these changes will be of anegligible nature, as compared with the total impedance, including thatadded by resistor R2.

Due to the method of pulse generation in accordance with the preferredform shown, the synchronizing pulse output forthcoming from clipper I5is twice the frequency of the master oscillator. As will later appear,this relation means that for the minimum required pulse width in theoutput of multi-vibrator I6, the period of the master oscillator must beequal to twice the time width of these minimum-sized impulses.Expressing this relation between the master oscillator period To and theminimum time width of desired pulses tw, To=2tw, and since therelationship between a period t and the frequency f to which itcorresponds is where F is the tfrequency of the master oscillator. Thus,by way of example, if a pulse width of microseconds were required for acertain purpose in the output of multi-vibrator I6, the fundamentaloscillator frequency would necessarily be:-

F -10=100 kilocycles As above-indicated in the discussion of Fig. 1, aninverter circuit I I is employed to produce two balanced sine waves forapplication to the fullwave rectifier I2. In the form shown, theinverter I I includes an amplifier T2 having an output Ila including aload resistor R1. It will be noted that the output is taken directlyacross the cathode and plate circuits of tube T2, and that thereforebalance with respect to ground may be regulated by a variable resistorR5 included in the cathode circuit to ground. By adjusting cathoderesistor R5 to equal in magnitude the load resistor R1, zeroamplification results in tube T2 and maximum balance may be obtained. Inthe form shown, load resistor R1 directly supplies input energy to thefull-wave rectifier. This rectifier may include a double diode T3symmetrically fed across a resistor R8, and the oath-- ode circuit maybe connected through a resistor R9 to substantially the midpoint ofinput resistor R8.

As above-indicated in general language, we consider it preferable forincreased timing accuracy that the timing of the pulses appearing in theoutput of differentiator I4 be determined solely by the time at whichthe sinusoidal wave from oscillator Ill crosses the zero axis, that is,by the cusp portions 23 of the rectified wave; see Fig. 10. Since thecusp timing is independent of voltage variations (the cusp representingzero voltage), a high order of pulse timing or frequency stability ispossible by utilizing this portion of the rectified wave. In order toachieve maximum pulse stability, however, the sharpness of the cusp waveform must be maintained. This latter requirement necessitates thathigh-frequency discrimination and distortion at the wave cusps be keptat a minimum, that is, that the circuit be as evenly responsive asfeasible to a relatively wide band of frequencies. To this end,

potentiometer R8 is connected as shown, and the.

resistor R9 is made small in order to minimize the shunting efiect ofthe input coupling to the following stage (differentiator l3) The twodifferentiator circuits I 3 and I4 are of essentially similar and knownform, and include amplifier tubes T4 and T5 having coupling circuitswhich constitute the difierentiating networks. These coupling circuitsmay be of the simple resistance-capacitance type, and in the form shown,include condenser CII and resistor RH for the output of the tube T4 ofdifferentiator l3, and condenser CI5 and resistor RIB for the output ofthe tube T5 of differentiator HI. The wave-form treatment, as energyfrom the rectifier I2 passes through differentiators I3 and I4successively, is indicated graphically in Figs. 1d and 1e. It willbeseen therefrom that the output of differentiator I4 as appearing acrossresistor RI8 comprises a series of extremely short impulses ofsuccessively positive and negative sense.

Since the form of the multi -vibrator I6 shown requires positivesynchronization impulses for operation, the output of differentiator I4is next limited through a clipping device I5 so as to produce a seriesof uni-directional synchronizing impulses. In the form shown, clipper I5includes a class C amplifier employing tube T6. As is well-known, inthis form of amplifier negative excursions of the input voltage pastcutoff cannot be reproduced in the plate circuit, and a limiting actionthus results. Inherent in the operation of tube T6 is the fact that aphase reversal occurs. Accordingly, the result of cutting out thenegative pulses in the output of differentiator I4 is to produce aseries of negative pulses in the output I5a oi clipper I5. Passage ofthis energy through another vacuum tube device is therefore necessary inorder to reverse the pulse phase and to produce the positive impulsesrequired for the multi-vibrator I6. In the form shown, this latter stageis a simple class A amplifier TI. Now, since the input to this stagewill be relatively high, tube T'I may be additionally employed forshaping purposes, that is, to limit the magnitude of output pulses dueto saturation in tube TI. The resulting pulses in the output of thisstage are thus at proper polarity for synchronization, but present theundesirable feature that they are delivered at a relatively highimpedance, as presented by the plate circuit of tube T1.

In order for these synchronized impulses to be delivered to themulti-vibrator circuit at low impedance, we choose to employ a knowntype of cathode follower device I8, which in the. form shown, includestube T8 from which the low impedance impulses are derived acrossresistor R28 in the cathode circuit. The cathode follower circuit mayalso serveadditional functions should the magnitude of impulse energyapp-lied to the input thereof be too great for proper synchronization ofthe multi-vibrator. To these ends and due to the step-down impedancetransformation from the input circuit to the output, voltage may bereduced with a minimum of distortion. Tube T8 may serve a furtherfunction should the input be of unduly large magnitude, in that, due toplate saturation and grid-current flow, amplitude limiting and furthershaping may result. It will be clear from the above-described circuitthat the output of this stage, as applied to a load through a co-axialline P1, is a series of regular synchronizing pulses of short durationand occurring at a frequency equal to twice that of the masteroscillator I9.

The multi-vibrator used may be considered to be ,of a dissymmetrica'ltype, that is, the time-censtant decay circuits of the input section aredissimilar 'to those used in the output or alternate section. One ofthese time-constant circuits is employed to control output pulse width,and the other to determine the recurrent frequency of the pulses whosewidth is :being controlled by the first of said circuits, as will laterbe, clear.

Referring to Fig. 3, the 'multi-vibrator i6 is shown'to include a doubletriode T9 comprising a triode section indicated generally by I andanother indicated by II. A resistance 30, capacitance 3|, andga furtherresistance 32, between the output circuit of tube section II and groundare, included in the time-constant circuit which will be seen to bedeterminative of the width of the desired pulse; and a resistanc 33,capacitances 34, 35, and a further resistance 36, between the outputcircuit of tube section I and ground are included in the time-constantcircuit which will hereinafter be seen to be determinative of thefrequency of recurrence of pulses derived from the multi-vibrator.

A better understanding of the operation of the multi-vibrator may be hadby reference to the various curves shown in Fig. 4. In this fig ure,curve a represents the series of synchronizing impulses supplied fromthe cathode follower 58 over the co-axial line P1, Figs. 2 and 3; curve19 represents the instantaneous voltage appearing on the grid of tubesection I; curve represents plate current for tube section I; curve 01represents instantaneous voltage appearing on the grid of tube sectionII, and curve e represents output current for tube section II. All fiveof these i curves have been drawn against time, and for ductive, wherebythis impulse is amplified andv at the same time its phase is reversed tomake it in effect an amplified negative im'pulse. Instantaneously thislarge negative voltage is applied to the grid of tube section II to biasthe latter below cutoff, whereby tube section II is renderednon-conductive. On the curves of Fig.

4, this reaction is illustrated on curve d by a large swing 38 of gridvoltage on tube section II below cutoff, and the resultant subsidence ofoutput current in this tube section to zero is indicated by the wall 39dropping to zero current in curve e.

As tube section I continues to conduct a large quantity of current, arelatively high voltage drop persists across resistance 36; and, as aresult of the circuit values of condensers 34 and '35 and resistance 33,a voltage begins to build up across resistor 33 so that the grid voltageof tube section II builds up in a sense approaching cutoff. In Fig. 4,this increase in grid voltage toward cutoff is shown by the portion 40of the curve of Fig. 4d. "Now, as the grid voltage in tube section II isthus building up towards cutoff, the synchronizing impulses applied tothe multi-vibrator circuit continue and are necessarily impressed uponthe voltage appearing across resistor 33. As the synchronizationimpulses are thus applied across resistor 33, they will be of reducedmagnitude, due to the fact that they have had to traverse certaincircuit impedance represented by condensers 3|, 34, and

various leakage resistance paths. Thus, on curve d theyhave beenrepresented as of reduced magnitude. The synchronizing impulses reachingthe gridof tube section II-will be of a positive sense, however, due tothe fact that they have reached this point directly, rather than bypassing through a -vac'uum tube device. They are accordingly shownpositively superimposed upon curve portion 40.

' Now, the magnitude of the synchronizing impulses when superimposedupon the voltage that fisbuilding up across resistance 33 (asrepresented by curve portion 40) is at first insuificient to carry thegrid of tube section II to a point greater than cutoff; but, as thisgrid voltage builds up, there will become a time when the superpositionof a synchronizing impulse upon a voltage that has built up acrossresistor '33 will be great enough to apply a potential greater thancutofi potential to the grid of tube section II. In the assumedillustration, this time occurs with the third synchronizing impulseafter the grid of tube section II was placed below cutoff, as will "beclear from Fig. 411.

Once tube section II is thus rendered conducthe assumed case willbe-thatindicated as 4 l may be greatly amplified by tube section II. This largeoutput may then be instantaneously applied to th grid of tube section Ias a large negative impulse. The magnitude of this negative voltageapplied across the grid of tubesection I may thus be great enough to cutoffconductivity of tube section I, as indicated by the sharp downwardswing of grid voltage in tube section I (see the port-ion 42 of curve I)of Fig. 4). Once tube section II has thus been rendered conductive, itwill remain so until the large negative voltage across the grid of tubesection I builds up in a positive sens to cutoff. The rate of thisbuildeup, it will be clear, is governed by the particular time constantof the circuit defined by resistor 30, capacitance'31, and resisto 32,as will be clear. Now, due to the fact that synchronizing impulses arebeing continuously applied to the grid of tube section I with their fullmagnitude A, tube sec-. tion '1 maybe rendered prematurely conductive,owing'to the superposition of impulses of magnitube A upon thepositively increasing negative voltage :across resistor 33. Thisphenomenon is shown to occur in Fig. 4b with the synchronizing impulsewhich next succeeds the impulse M which caused the grid of tube sectionI to be biased well below cutoff. Oncetube section I again becomesconductive, the grid of tube section II is immediately biased beyondcutoff and the above-described cycle of operation repeats itself.

It will be noted that, in the form shown, output from th multi-vibratoris taken in line 44 from across resistor 36; in other words, output is'taken from tube section I. It follows from the above discussion ofmulti-vibrator action that this output current will have the form shownin Fig. 40. that is, it will "be characterized by relativelylong-duration impulses with small interus vals between them. If it weredesired to obtain small impulses with relatively large intervalstherebetween, output should be taken across the late circuit of tubesection II, that is, by connecting line .44 acrossresistor 32 instead ofacross resistor 3.6 as shown. Multi-vibrator output would-then presentthe wave form shown in Fig.

Presu-ming that multi-vibrator output is derived acrossresistor 3:2 toyield a series of regu- .larl-y' spaced relatively short-durationimpulses,

tive, the applied synchronizing impulse, which in it may readily be seenhow in accordance with the invention the periodicity of impulserecurrence may be varied while maintaining impulse duration constant.This extension of impulse separation may be obtained, for example, byincreasing th resistance 33 across which voltage applied to the grid oftube section II builds up. Such an increase in the resistance 33 willhave the effect of changing the slope of the curve portion 40 of Fig. 4dso as to correspond, for example, with the line 45. Now, when thesynchronizing impulses are superimposed upon this alternate curveportion 45, -it will be clear that the third synchronizing impulse afterthe grid of tub section I! has swung below cutofi will be ofinsufiicient magnitude when superimposed upon. curve section 45 torender tube section II conductive. In the form shown, however, the nextsucceeding, that is, the fourth impulse, will be of suificient magnitudeto render tube section II conductive and thus immediately to cut off theconductivity of tube section I, as will b clear. Operation thereafterwill be of an analogous nature to that above described in connectionwith the full-line showings of curves 41) through 4e. This alternateoperation is shown, for example, in dot-dot-dash lines to bedistinguishable from the other fullline showings.

It will be clear from the above discussion that appropriate change inmagnitude of any of the parameters affecting the voltage build up acrossresistor 33 may have the effect of changing the recurrent frequency ofoutput impulses. It is further to be noted in this connection that thewidth of pulses in the multi-vibrator output may if desired bemaintained precisely the same regardless of how the periodicity ofrecurrence varies. This feature follows from an appreciation of the factthat the time-constant circuit controlling output pulse width may alwaysbe maintained substantially the same, so that pulse width may always bedetermined by two synchronizing impulses of the same accurate timespacing.

In an analogous manner, the width of output impulse may also becontrolled to be any desired multiple of the synchronization impulserepetition frequency 2Fo. To this end, a variation in the capacitance 3|may have the effect of increasing the build-up time of bias voltageimpressed on the grid of tube section I as tube section II isconductive. This build-up time may be increased. so much that when thesynchronizing impulse which succeeds the one which rendered tube sectionI nonconductive comes along, the magnitude of this succeeding impulswill be insufiicient when superimposed upon the voltage that has by thattime been built up across resistor 30 to render tube section Iconductive. It will thus remain for the next succeeding, or perhaps astill later, impulse to render tube section I conductive. It isaccordingly clear that impulse width may be controlled to be equal toany integer multiple of the synchronizing impulse repetition frequency.

An alternate method of controlling either pulse repetition frequency orthe width of output pulses from the multi-vibrator may be to control themagnitude of synchronization impulses applied to the grid of tubesection I. Such control may be included within the circuit of cathodefollower l8, as will b clear, and may for example b in the nature of avariable tap on the input resistor R21 of tube Ta. Should this controlbe effective to reduce the magnitude of applied synchronization impulsesto a great enough extent, tube section I may fail to go conductive afteran interval equal to the period between synchronization impulses and maythus go conductive after one or more synchronizing impulses have beenimpressed on this grid.

It will be clear that, in order to facilitate an understanding of theoperation of the multi-vibrator in accordance with features of theinvention, the showings in Fig. 4 have been greatly exaggerated, thatis, the impulses present in the output of the multi-vibrator have beenshown to be excessively large with respect to the intervals separatingthem. In actual practice, it is contemplated that greater separationintervals may be employed merely by appropriate selection of the circuitconstants and current magnitudes present in the multi-vibrator circuit.For example, in an actual embodiment of the invention, we have been ableto obtain output impulse recurrent frequencies of from 500 to 6000cycles while maintaining the pulse width constant over this entirerange. This result, it may be noted, was obtained when a quartz crystaloscillating at 200 kilocycles was employed.

Although the current output wave form from the multi-vibrator has beenshown in Fig. 4 to be very regular, that is, zero current for a whilefollowed by a constant maximum, conceivably such regularity may not be afact. Accordingly, in order to assure that a better square-wave outputwill be obtained, we propose to us appropriate wave-shaping elements.

In the form shown the multi-vibrator output is applied to shaper stageIt by way of a capacity coupling 46. Referring to Fig. 3, shaper it isseen to comprise an ordinary amplifier tube Tm. The input circuit oftube T10 is provided with adjustable biasing means 5'! whereby the tubemay be preferably biased, beyond cut-off, thus performing a clippingaction to eliminate any circuit noise or transient phenomena occurringnear the base of square-waves generated by the multi-vibrator. Tube T10also preferably has a high-p4 characteristic so that further shaping maybe obtained due to saturation effects limiting the top of the squarewaves to a substantially uniform magnitude.

In the form shown the adjustable biasing means 47 includes a fixedresistor 58 adjustably tapped to a potentiometer 49, which is connectedacross the biasing source (not shown). t will be noted that in actualitythen coupling condenser 46, resistor 48 and potentiometer 49 form partof the time-constant circuit which in the assumed illustrative casecontrols the longer of the two recurrent intervals defined bymulti-vibrator action, If adjustment is contemplated in the magnitude ofthe bias voltage for tube T10, it is considered preferable that suchadjustment be effected with a minimum of change in the overall impedanceof elements 48, 48, and 49. Accord ingly, resistor 48 is preferablylarge compared with the impedance of potentiometer 49.

As shown output from the shaper stage i0 is taken from the anode circuitof tube T10. There is thus a reversal in phase (polarity) of resultantsquared pulse energy, and in order to obtain positive wave-forms a phasereverser 2?) similar to phase reverser I! may be employed. As in thecase of phase reverser I'l, phase reverser 20 may include an ordinaryamplifier tube T11 capacitance-coupled to the output of tube T10. Atthis stage it may be observed that further shaping of the squared-wavesmay be effected by taking advantage of the fact that the input waveformis negative, y operating tube T11 at substantially zero bias andapplying relatively large -values of input voltage, clipping of thenegative maxim'a may take place at cutoff, whereby both the bases and"the crests of'the resultant positive squared-- waves are defined byclipping (cut-on) action;

; Next and in order that the squared-waves may be supplied for anydesired purpose at relatively low impedance, a cathode followeri'l',similar to cathode follower 18; may be employed. The circuit for cathodefollower 21 may thus comprise a conventional amplifier tube T12capacity-coupled to tube T11, and output for a desired load Pi may bederived without reversal of phase across resistor d common to 'the inputand output circuits of tube T12, aswillbe clear. 7

' Many useful applications "of the above-described device will doubtlessoccur to those skilled in the art. These' applications may includereceiver blocking, wave-blanking, difierential delay circuits, and thelike. One significant application will be briefly described.

As indicated at the outset, the invention iscontemplated to haveparticular utility in the field of obstacle, particularly aircraft,locating apparatus. According to this type of device, as fully describedin the above-mentioned copending patent applications of Messrs.Busignies and Labin, an impulse transmitter is employed periodically toradiate impulse energy. For each impulse transmitted, provided there isa reflecting object within range of the apparatus, a reflection of thisimpulse may be detected at an instant of time later than the instant oftransmission by an amount proportional to the distance from theequipment to the reflecting object. The receiving equipment includesmeans for detecting the refiected impulses and an indicating device,preferably a cathode ray tube having at least two electron beam controlsystems. One of these control systems may be a conventionaldeflectionsystem to which sweeping voltages, synchronized with the periodicrecurrence of transmitted impulses, may be applied. The other of thesecontrol s sterns may be another deflection system to which energy fromdetected received signals may be applied.

The teachings of this invention may be applied to obstacle detectionsystems of the abovedescribed character in substantially the followingmanner. Energy characterizing the synchronizin impulses which rendertube section I of multivibrator non-conductive and simultaneously maketube section II conduct may be employed also to synchronize or energizethe impulse transmitted so that impulse energy is transmitted only atthese particular instants of time. Such a synchronizing signal could beobtained, for example, by sending output energy from either tube section(I or II) through a differentiator circuit, whereby sharp alternatelypositive 51 0f Fig. 4b; asobtaine'd for example by a high impedanceconnection across the inputof tube section I, be amplified,-appropriately polarized;-

" represented by the interval of non-conductivity of tube section I.Accordingly; if received: if F flections of transmitted impulses bedetected within the interval of time during which. tube section Iisnon-conductive, there will be observed'on the screen a needle-likeindication transverse to the distance or time interval sweep scale; andthe lateral disposition oi this needle-like indication with repect' toends of the distance scale may be indicative of distance tothe-reflecting object as will be clear. r

If it should happen that the reflecting object is relatively far away,the interval between successive synchronizing impulses may not allowsufiicient time for transmitted impulses to reach the object, bereflected, and then be detected by the receiving equipment. In such anassumed case the transverse needle-like deflection representing thereflecting object will appear at one end of the distance scale, andadjustment will be necessary before the distance to the object may becorrectly determined. Such adjustment may be made very simply by makingany of the abovenoted adjustments to change the period ofnonconductivity of tube section I. A simple expedient would be toincrease the time constant of the circuitdefined by elements 30, 3|, and32 so that instead of the period of non-conductivity of tube section Ibeing merely the period between synchronizing impulses, it may beprecisely the period of every two, three, four, etc. of thesesynchronizing impulses, as will bev clear. In this manner, it would bepossible effectively to magnify or enlarge the range of theobstacle-detection apparatus as desired, and at the same time always tohave a precisely calibrated distance scale on the cathode ray screen,due to the high accuracy of the stable timing source, quartz oscillatorII).

It will be appreciated that we have disclosed means and methods forgenerating synchronizing impulses having a high order of stability andaccuracy of recurrence. These pulses may be highly useful for accuratesynchronization of sawtooth generators, multi-vibrators, timers, andother devices. In a specific embodiment these synchronizing impulses areemployed to produce other pulses of highly precise constant width,adjustable as desired to an integer multiple of the synthen negativeimpulses would result, and then clipping so that whichever of these setsof impulses characterized the above-noted instants of time may remainfor application to the transmitter unit.

Concurrently with the use of multi-vibrator output energy just noted,the periods of nonconductivity of tube section I (i. e. the shorterintervals) could be employed accurately to define a distance scale onthe cathode ray indicator tube. To this end it is suggested thatsweeping energy proportional to the change in voltage represented by thesolid line voltage build-up curve chronizing impulse period. These otherpulses have the further feature of recurring at an easily adjustedsub-multiple frequency of the frequency of the synchronizing impulserecurrence, and have been shown to have utility in specific applicationto obstacle-detection apparatus.

Although the above specification has dealt with specific preferredembodiments of the invention in considerable detail, it is to beunderstood that these embodiments are purely illustrative and that manyadditions, adaptions, and omissions may be made fully within the scopeof the invention.

What we claim is:

1. A device for generating periodically recurrent impulse energycharacterized by impulses of accurately defined duration comprising:means for generating a regular series of relatively short accuratelytimed synchronized pulses, a multivibrator having two dischargesections, each having an input circuit, means to apply said synchronizedpulses to one of the input circuits, first, to render in response to asynchronized pulse one of the sections conductive and the othernon-conductive, and second, to effect in response to a latersynchronized pulse the reverse operation, means providing a timeconstant for the input circuit of said one section to terminate theconduction therein upon the occurrence of a synchronized pulse apredetermined interval after initiation of conduction thereby generatingan impulse of given duration, means providing a time constant for theinput circuit of said other section to terminate conduction therein uponthe occurrence of a synchronized pulse a selected interval afterinitiation of conduction to determine the frequency of the generatedimpulses, means 12 to independently vary the value of said time constantmeans, and means to withdraw the resulting periodically recurrentaccurately timed impulse energy from said multivibrator circuit.

2. An impulse generating device according to claim 1 in which saidsynchronized pulse generating means includes: a stabilized sine Waveoccillator means, a full wave rectifier means coupled to said oscillatorto produce a series of accurately and equally time spaced cusps, a firstdifierentiator circuit coupled to the output of said full Wave rectifiermeans, a second differentiator circuit coupled to said firstdifierentiator circuit said differentiator circuits sharpening the cuspsof the rectified sine wave, and clipping means coupled to the output ofsaid second differentiator circuit for producing a unidirectional trainof accurately and equally time spaced instantaneous pulses.

1 EMILE LABIN.

DONALD D. GRIEG.

